Interesting topic.
Some of it is due to sheer numbers...
There are what, 1500 players (give or take) in the NFL total?
More people equals more fukkery.
The NBA has about 450, with 20 or 30 players getting drafted or shuffled through the NBA and other leagues (D-League, Euroleague, etc) every season.
And since there are so few spots in basketball and all 12-15 are under a media microscope, you have
waaaayy less room for fukkery. And with the NBA being the leader of social media/league integration, one incident rumor will be blown up within an hour.
One slip up, and you can be gone.
And the NFL markets teams rather than individuals, so the 7th string WR that got a DUI won't get as much pub as the 8th man on an NBA team that gets interviewed every night getting caught saying "f**k feminists" on someone's camera phone.
I have more theories, but they'll fill a damn page.
I might add some more later.